Butterfly OR Gate Valves - Waterworks application 2

[Kandeel76]

Hello All ,

When we speak about isolation manual valves there are many types, I choose two (2) of them as butterfly double eccentric & gate valves , max working pressure 16 bars for water application,sizes from 2" up to 80", both valves in ductile iron bodies.

My question : what are the advantages and disadvantages between them? , I see different pipelines for one water application they use butterfly and same application in another project use gate!!
For me, I want to know the main differences between butterfly and gate, as flow rate which higher? also pressure losses, valve torque,valve cavitation, etc.....

Commercially, I know that double eccentric butterfly less than 12" is mostly higher price than gate, above 12" butterfly will be cheaper than gate also lower dimensions than gate.

Thanks in advance for appreciated professionals


Regards,

Kandeel

 

[rconner]

If you do a search of all forum archives you will find many past and lengthy thread discussions of this subject e.g. with search keywords "butterfly gate valves". While I guess both types of valves can be used for simple/basic "isolation", in the contemporary environment one increasingly important difference in some applications is lesser head loss, and the somewhat exclusive ability in the future to pass pigs, men and/or all manner of equipment also when necessary through a gate valve passageway.

 

[gerhardl]

Based on Scandinavian experience, and with weight on cost/lifetime considerations, some general rules can be given, but note that the choice between the two seems to be some kind of 'religious issue' for some decision makers.

Presumtion: both valvetypes selected from top producers, high quality, longterm operational references.

Overweight of soft sealing gatevalves often when:

Lower pressure (and pressure classes) lower dimensions (up to 150mm, 200mm (more seldom up to 300mmm or above). Valves with easy access, valves on lower dimension distribution nets, hand operated valves. Valves where pigging ar required. Less automated, but used both with el. and pneumatic.

Double eccentric BFL valves in overweight for:
Automated valves, valves often operated, valves very seldom operated, valves with difficult access, larger valves, valves for higher pressures (within the given range), critical valves, emergency shutdown valves.

Presumption: Double eccentric BFL valves, with gear of top class (sliding crank best) with easy rebuilding from hand operation to el. actuator. (El. actuator preferred if automated but also pneumatic selected - great discussion between the two especially for UV- treatment processes for drinking water).

Double eccentric BFL should in my opinion absolutely be selected and preferred when economical possible.

Some of the largest,well renowned waterworks/district distribution organizations has from longterm experience required all valves above 150/200 mm to be double eccentric BFL (not gate).

Other markets or users may have different opinions.

You should especially note that within both types (gate and BFL) there are seemingly 'equal' valves with vastly different constructional details, quality and performance and standtime.

Also pressure loss will vary with the single details, but will seldom be significant.

I have seen total pressure loss be discussed in detail for UV-treatment plants with BFL valves (required somewhat throttling) at low flow and low pressures, with no problems popping up.

Pressure losses for good constructed double eccentric BFL valves are lower than for centric valves.

One tip is perhaps to open for valvetype alternatives and technical improvemets, information/argumentation and references from distributors, or even preliminary technical offers to qualify for final bidding.

Remember: lifetime cost, not buying cost, are the most important criteria. Do not write specifications to exclude newer improvements or higher buying cost.

Good luck!